Variation in thermal and hydrotime requirements for seed germination of Chaco seasonally dry forest species in relation to population environmental conditions and seed mass

Abstract

Thermal and hydrotime requirements for seed germination can vary with the species, environment in which the seeds developed and/or seed mass. We investigated seed germination responses to temperature and water potential of Aspidosperma quebracho-blanco, Bulnesia retama, Parasenegalia visco, Parkinsonia praecox and Tecoma stans, all of which are native tree species of Chaco seasonally dry forests in northwest Argentina. We determined inter-and intraspecific variability in seed germination through thermal and hydrotime models and correlated model parameters with environmental variables of seed provenance and seed mass. Seeds of all species germinated to high percentage over a range of temperatures. Seeds of A. quebracho-blanco, P. praecox and T. stans were more tolerant to water stress than those of B. retama and P. visco. Thermal and hydrotime parameters for germination varied amongst species and populations. There was a negative correlation between thermal (θ T(50) ) and hydrotime (θ H ) constants and base temperature (T b ) and water potential (Ψ b(50) ). Seed mass correlated negatively with T b and positively with θ T(50) . Species and populations were grouped according to thermal and hydrotime parameters and seed mass but not according to seed provenance. These results suggest that seed germination traits related to temperature, water potential and seed mass are species specific, and the variations within a species are probably due to a high phenotypic plasticity. These species showed a complex set of germination strategies that give them a competitive advantage in different environments, depending on dispersal time, seed mass and local environmental conditions during the germination period.

Variation in Seed Dormancy of Chaco Seasonally Dry Forest Species: Effects of Seed Traits and Population Environmental Conditions

“…For the other species, the low germination percentage in all light and temperature conditions indicates the presence of seed dormancy and the requirement for exposure of seeds to specific environmental conditions to promote dormancy-break and germination. Similar results have been reported for these species and other species characteristic of the seasonally dry Chaco forests of Argentina [38,40]. This interspecific variation in seed traits and seed germination…”

“…In our study, we also found high intraspecific variability in seed traits and seed dormancy and seed germination. Except for P. praecox and S. lorentzii, the study species exhibited intraspecific variability in most seed traits, probably due to a high phenotypic plasticity [12,38,43]. For seeds of S. mistol and S. lorentzii, (with PD), the response to dry storage differed among populations, which may be associated with differences in the intensity of PD and/or sensitivity to dormancy-breaking factors [18].…”

“…Darkness was achieved by wrapping dishes in aluminum foil, and germination was recorded once at the end of the experiment. Temperature regimes were selected based on average temperatures occurring in the field during the summerautumn months, which is the natural germination season [38]. At the end of the germination tests, when no additional germination had occurred in light for 2 weeks, a cut test was conducted to determine the viability of the non-germinated seeds (soft or firm, i.e., dead and viable, respectively), and the total number of viable seeds per replicate was calculated on the basis of the total number of firm non-germinated seeds + the germinated seeds.…”

“…The broad objective of our research was to study seed dormancy of these six Chaco species, evaluating their inter-and intraspecific variability in relation to seed traits and environmental variables. All these species can grow in each of the three kinds of Chaco forests, but due to differences in environmental conditions in the forests it is possible that seed dormancy and seed traits differ among species and/or populations [38]. Our first hypothesis was that Anacardiaceae, Fabaceae species (except for G. decorticans that has ND seeds [17]), and Rhamnaceae have seed dormancy (PY and/or PD).…”

The Impact of Water Potential and Temperature on Native Species’ Capability for Seed Germination in the Loess Plateau Region, China

“…One major environmental element that can control enzyme activity and either stimulate or prevent the generation of hormones that influence seed germination is temperature [ 15 , 19 , 20 , 21 ]. The germination responses of seed lots to temperature can be characterized through three cardinal temperatures [ 22 , 23 ]: a base temperature ( T b ), below which the seeds do not germinate; an optimal temperature ( T o ), at which the process proceeds at its fastest pace; and a ceiling temperature ( T c ), above which the process is stopped [ 24 , 25 , 26 ]. These cardinal temperatures, T b , T c , and T o , are associated with the range of ecological and geographic circumstances to which a particular species has evolved, and serve to couple the timing of germination with favorable conditions for subsequent growth and development [ 27 , 28 ].…”